There exists many applications where the control of an operative element such as for example a blower, heater, light, pump, etc., is regulated by a change in a controlled situation or environment. An obvious example of this is in home heating and cooling whereby a thermostat is used to activate heaters and air conditioners at appropriate temperatures and deactivate them at others.
In certain applications the changes may be gradual or fast it is desirable to accurately and quickly detect such changes in the controlled environment and accordingly compensate for the change. In this regard, the sensor should be capable of detecting the change and accordingly signalling the operative element to perform the appropriate compensating function. However, the sensitivity to enable it to accurately detect such changes may result in rapid on-off oscillation about a cut off point or allow for noise to unduly influence the operation of the system.
Further, rather than compensate by merely signalling the operative element to go on or turn off at a set level, it is often desirable to have the operative element activated in a manner proportional to the change in the controlled environment, so as to conserve energy. Such a situation is that as shown in FIG. 4, which involves the use of a greenhouse to collect thermal energy for heating an attached building. To distribute the collected heat, a blower may be utilized to circulate the heat between the greenhouse and the building thereby decreasing its overall energy costs. If necessary to preserve plants or for other reasons desired, the heat in the building at night might be used to compensate for any cooling in the greenhouse taking place during that time. An accurate interrelation between the operation of the fan or blower and the level of thermal energy in the greenhouse would be advantageous in the effective use of such thermal energy in heating the building.
Accordingly, it is an object of the invention to provide a device which accurately senses the changes in a controlled environment and provides an output capable of controlling the activities of an operative element in proportion to the changes involved.
It is another object to provide for an accurate switching about a predetermined cutoff point of the operative element thereby preventing rapid on-off oscillations thereabout and to prevent noise from unduly affecting the operation of a system.
A further object is to provide for such a device to control a fan or blower capable of circulating the air in a greenhouse or other thermal collecting means so as to maintain a constant level of heat therein whereby as the temperature of the greenhouse changes, it is sensed by said device and the blower is activated to a degree proportional to the change in temperature so as to circulate the heated air and thus distribute the collected heat. In this regard, the blower speed increases as the temperature increases above the set point. This allows for: the greenhouse to be kept at the lowest practicable temperature during the day to minimize its heat loss; a low amount of energy to be expended in blower operation during periods of low solar gain; the use of a large capacity blower so that during periods of high energy gain, all of the energy may be realized while preventing overcooling or rapid cycling during average and below average days; increasing the overall system efficiency by the lowered temperatures, increased blower capacity, and decreased power usage by the blower. In addition, an advantage in this particular application is the fact that with a lower blower speed, the noise resulting from the blower is greatly reduced.